In recent years, the number of vehicles that can use alcohol fuel, such as flexible fuel vehicles (FFV's), tends to increase. In an internal combustion engine that uses alcohol fuel, the amount of fuel injection is larger and the volatility of fuel is lower than in an internal combustion engine that uses gasoline. Therefore, injected fuel is likely to adhere to an intake passage or a wall surface in a cylinder, and as a result, the amount of fuel that is mixed with engine oil (an oil dilution amount) also tends to increase. Accordingly, in the case where alcohol fuel is used, it is preferable to employ a PCV mechanism or the like.
As disclosed in, for example, Patent Document 1 (Japanese Patent Application Publication No. 2009-138571 (JP-2009-138571 A)), the PCV mechanism introduces blow-by gas in a crankcase into an intake system, and the amount of blow-by gas introduced into the intake system is adjusted in accordance with an intake negative pressure. Thus, the fuel that has evaporated from engine oil can be burned together with the mixture.
Incidentally, the applicant recognizes documents cited below including the above-mentioned one as those associated with the invention.